Security Bypass Affecting Open this link in a new tab package, versions [,2.1.22) [3.0.0,3.1.8)

  • Exploit Maturity

    Proof of concept

  • Attack Complexity


  • Integrity


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  • snyk-id


  • published

    9 Sep 2020

  • disclosed

    8 Sep 2020

  • credit

    Matt Langlois of Github Security Team

How to fix?

Upgrade Microsoft.AspNetCore.App to version 2.1.22, 3.1.8 or higher.


Microsoft.AspNetCore.App is a package that provides a default set of APIs for building an ASP.NET Core application.

Affected versions of this package are vulnerable to Security Bypass. The ASP.NET Core cookie parser decodes entire cookie strings which could allow a malicious attacker to set a second cookie with the name being percent encoded. The security update addresses the vulnerability by fixing the way the ASP.NET Core cookie parser handles encoded names. This CVE also affects Microsoft.Owin due to it using a similar cookie parsing mechanism.